When driving a rail vehicle, vibrations and the subsequent emission of acoustic energy in the form of acoustic waves occur due to dynamic effects in contact of a wheel with a rail. In the audible frequency range, we call these waves as sound. If this sound is unwanted, it is called noise.
To reduce vibration and noise, various passive damping elements, generally known as dampers, are applied in the rail wheels, which are connected with the wheel by means of screws, rivets, adhesive bonding, vulcanization, spacer elements and the like.
So far, various types of dampers have been applied to the rail wheels. Dampers of annular shape are known, which can divided further by a set of cuts into more parts, wherein these parts may be partially divided further by a set of cuts. The so made dampers are disclosed for example in documents FR 2,569,271 or U.S. Pat. No. 5,734,133. Typically, such dampers comprise one or more layers of metal sheet and a damping material. Mounting of the wheel dampers to a wheel is realized either by means of bolted connections via through holes in the wheel, in its reinforced area between the rim and the plate parts of the wheel or the dampers are mounted via additional fastening elements to a shaped groove of the wheel rim.
A disadvantage of these dampers, mounted to the rim part of the wheel, is that the additional fastening elements, attached, for example, through a shaped groove or through flexible spacer members in the wheel, must ensure a very good transmission of vibrations from the wheel rim to the damper. If the quality of the vibration transmission decreases, the efficacy of the damper decreases simultaneously. So, these dampers are not very efficient in wheels, in which the dominantly oscillating part is the rim one. Due to the additional fastening elements, the price of such solutions is growing. A disadvantage of a damper mounted to the wheel rim, in which threaded parts are made, is also that for security reasons this solution is applicable particularly only in the rubber-sprung wheels. In the dampers, which are divided into multiple parts, wherein, there are gaps between the individual parts, it occurs that the larger are the gaps, the less the damper prevents the passage of sound waves. Another disadvantage of these dampers is that to reach sufficient damping, in the critical and higher frequency of the damper an effective emission of the acoustic energy by the damper itself must not take place, what depends on the geometry and material composition of the damper and represents a certain limiting factor for the construction of a damper.
Also, hitherto, steel rings, typically of circular or rectangular cross section, inserted into the circumferential grooves at the inner diameter of the wheel rim, have been applied as a shock absorbers in certain railway wheels. A design of such damping steel ring of circular cross-section is shown, for example, in the document GB 445,124. Usually, fixing of the ring end portions is made of a welded joint. These steel rings reduce vibration level by dry friction in contact with the groove of the wheel rim.
A disadvantage of the steel rings as dampers is that the damping effect is closely related with the bracing of the rings and thus with the contact circumstances with the wheel at their periphery, and subsequently with the amount of energy loss by friction during the oscillation of the wheel. It is technologically complicated to ensure optimal bracing of the rings in this design. In addition, damping by rings will begin to show up more significantly only when the own frequency of the wheel is higher.
Also, the resonantly tuned dampers, mounted on the board or the ring parts of the wheel, used to reduce vibration levels of a wheel for the selected shapes of wheel vibrations, are known and have been applied in practice. A design of such dampers is disclosed for example in the GB document No. 293,657.
A disadvantage of the resonantly tuned dampers is that their efficacy depends on accurate frequency tuning to reach the own frequency of the wheel and the suppressed vibration shape corresponding to it. The wheel wears during operation causing a change in its own frequency, and thus detuning of the damper takes place and its effectiveness is reduced. In addition, the wheel is driven over a wide frequency band, which band includes more than one or two major forms of oscillations of the wheel, on which the resonance damper is tuned, what can significantly reduce the effect of the damper. Because of the rolling of the wheel, splitting of the own frequencies for all shapes of vibrations takes place, with one or more nodal diameters and formation of running waves in the circumferential direction of the wheel takes place. This prevents accurate tuning of the resonant frequency of the damper.
Up to now, shock absorbers, which are glued or vulcanized on the surface of the wheel, were also applied in the operation of railway wheels. A design of such shock absorber is disclosed, for example, in EP 0 872 358 A1. Typically, dampers consist of a layer of viscoelastic material and a metal layer in the direction from the wheel surface. These dampers absorb mechanical energy produced by oscillation of a wheel, particularly by the shear deformation of the viscoelastic material.
A disadvantage of these dampers, which are glued or vulcanized to the surface of the wheel, is that the damper must be well connected with the entire contact area with the wheel, what is technologically rather challenging. In case, the connection with the wheel is not flawless, there will be a decrease in the effectiveness of the damper. Because of the deformation stress in the contact area of the damper with the wheel during operation, the connection may be partially disintegrated, what causes reducing of the effectiveness of the damping, or eventually, the damper may be ripped off the wheel. Also, the use of the damper only for the lifetime of the wheel is a limiting factor.
Also, multilayer sandwiched dampers consisting of mutually interspersed thin layers of metal sheet and damping material are applied to the damping on the railway wheels. Designs of such dampers are disclosed for example in EP 0 047 385 B1 and DE 31 19 960. For example, the dampers are attached using a shaped groove in the wheel rim, through connecting elements by means of bolted joints, or they are clamped over the threaded portions by means of bolted joints in the transition zone of the plate to the rim. The damping principle consists in the energy dissipation by shear deformation of thin layers of the damping material, which energy is produced by cyclic bending of the damper during the wheel vibration.
A disadvantage of the multilayer sandwiched dampers, mounted beneath the wheel rim, is that they are less effective when the rim of the wheel oscillates dominantly. In attaching of dampers over the shaped groove in the rim of the wheel, it is difficult to ensure good contact of dampers, or fasteners eventually, with the wheel due to manufacturing tolerances of the wheel rim diameter. If a good contact of the dampers with the wheel, and thereby transmission of the vibrations into the dampers, is not ensured then decrease in the effectiveness of the damping takes place. Also, production of the shaped groove in the wheel rim is technologically demanding, leading to an increase in the costs in the case this solution is adopted. During operation, pushing away of the contact surfaces of dampers may also occur, leading to a decrease in the efficiency of the damping.
In some cases, the support members were applied on the wheels for attachment of the dampers, which members are fastened to the wheel by elastic bracing of the end portions of these members. The dampers are attached to the supporting members by bolts. A design of the attachment of the support members and the dampers is disclosed for example in the document DE 198 32 266.
A disadvantage of this solution of the damper attachment is that with regard to the manufacturing tolerances of the wheel a good contact of the bearing members with the wheel is not ensured, what results in reducing of the vibration transmission from the wheel to the dampers, and thereby also in reducing of the damper effectiveness. Also, considering the directions and points of action of the expansion forces from the resilient members and the relatively high bending stiffness of the support members, there will not be any ideal abutment of the support members around the whole circumferential contact with the wheel, what again leads to a reduction in the transmission of vibrations from the wheel to the dampers and to the subsequent decrease in the effectiveness of the dampers. A disadvantage, appears to be also the relatively high manufacturing costs of the support members.